This application claims the priority of German Patent Application No. 198 01 166.0-21, filed Jan. 15, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a motor vehicle steering shaft having two shaft sections which are telescopically guided in one another. The shaft sections have corresponding profile cross-sections, between which at least one row of roller elements in each case arranged in the axial direction and is fitted in while creating a rotary fit between the profile cross-sections.
German Patent Document DE 35 13 340 C2 discloses, a driver connection between a hub and a shaft section guided therein, both of which having several longitudinal grooves, each corresponding in pairs and in which ball sets are arranged. A ball set consists of a row of balls which are arranged in the axial direction and which are pressed in between the hub and the shaft section into two corresponding longitudinal grooves forming a bearing seat, which is open in the axial direction, for the corresponding ball set. The pressing-in operation takes place while plastically deforming at least one of the components and establishes a connection which ensures a torque transmission and axial adjustability. A falling-out of the balls is to be avoided.
European Patent Document EP 0 629 540 B1 (corresponding to U.S. Pat. No. 5,544,542) discloses, a connection between two shaft sections of a motor vehicle steering column. A fixing of the shaft sections with respect to one another is provided by means of several form-locking cast resin packings and a square section which is form-lockingly guided in the rotating direction. A ball, which is fitted in during the manufacturing while a shaft section is plastically deformed is arranged between the shaft sections for ensuring electric contact. In the event of a crash, while the shaft sections are axially displaced with respect to one another, energy absorption is carried out by means of a further plastic deformation of a shaft section.
It is an object of the present invention to provide a motor vehicle steering shaft of the aforementioned type, wherein in addition to a torque transmission between the shaft sections, by means of particularly simple devices, a high occupant safety level is achieved in the event of a vehicle impact.
This and other objects are achieved in that an axial stop is assigned to the end-side roller elements of the roller element rows respectively. The axial stops are positioned on opposite shaft sections, at least one axial stop being plastically deformable. As a result, a form-locking fixing of the roller element rows is achieved in the axial and circumferential directions by means of a deforming of the at least one plastically deformable stop in the event of a crash-caused axial displacement. The movement energy is thereby destroyed. As a result of the arrangement of a suitable number of roller element rows, the connection can be adapted to possible cases of stress. In addition, by means of the special design of an individual stop, particularly by the dimensioning of the course which is radial relative to an axis of rotation of the steering shaft, the energy absorption capacity can be influenced.
As a further development of the invention, at least one axial stop is constructed as a transition from a circular to a noncircular profile cross-section of the concerned shaft section. Such a stop can be produced in a particularly simple manner.
In a further development of the invention, at least one axial stop has several steps of different courses in the radial direction which follow one another in the axial direction. As the result, a stepped deformation can be achieved of the shaft section having the stop as well as of the opposite shaft section because, when the pertaining balls roll over the stop, a deformation work is carried out which depends on the height of the radial expansion of the stop.
In a further development of the invention, a spacer, which is aligned in the axial direction of the shaft sections and is constructed as a separate structural element, is arranged between two balls of a roller element rows. The spacer does not have to be provided for a torque transmission between the shaft sections if the remaining balls are sufficient for the torque transmission. It is particularly useful for reducing the weight while ensuring a sufficient axial guiding of the shaft sections with respect to one another by the remaining balls which have a sufficient axial distance from one another.
In a further development of the invention, the spacer is constructed as a cylinder which has a diameter which corresponds at most to the diameter of the balls. Such a cylindrical spacer can also be used for the torque transmission. The cylinder may completely replace several balls.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.